Physical therapy regimens prescribed for patients with patellofemoral pain commonly emphasize training the vastus medialis obliquus (VMO) in an attempt to improve deficits in VMO strength and delays in VMO activation that have been noted for patients. The goal of training the VMO is to decrease the pressure applied to areas of overloaded cartilage in the lateral half of the patellofemoral joint, although biomechanical data showing the benefit of improving VMO function is lacking. The proposed study is based on the hypothesis that improving VMO function reduces the compressive force applied to the lateral cartilage of the patellofemoral joint and reduces patellofemoral pressures, but that these changes can be small due to anatomical factors or cartilage degradation. An in vitro experimental study is planned to determine how improving VMO strength and timing alters the pressure distribution. During simulated knee function with a weak VMO, a delay in VMO activation and a typical force applied by the VMO, pressure sensors will measure the patellofemoral pressure distribution for eight knees. Computational models will be created to represent the knees tested experimentally, and the computational and experimental data will be compared to validate the computational modeling technique. Computational models will also be created to represent the symptomatic knees of 10 patients with patellofemoral pain. The models will be used to computationally investigate the influence of VMO strength and timing on the patellofemoral pressure distribution. The models will allow for a more realistic representation of in vivo quadriceps loading and characterization of how anatomical factors and cartilage lesions influence the biomechanical changes associated with VMO training. This study will provide data that can be used to assess the efficacy of physical therapy regimens that focus on training the VMO and identify patients that are least likely to benefit from VMO training. Relevance: Physical therapy fails to reduce pain felt around the knee cap in approximately one third of patients. Although physical therapy regimens focused on training the inner quadriceps muscle are commonly employed, the benefit of this approach has yet to be established. The proposed study will utilize testing of cadaver knees and computational analysis of patients with knee pain to determine if training the inner quadriceps muscle effectively relieves pressure applied to cartilage within the knee. [unreadable] [unreadable] [unreadable] [unreadable]